move SkChecksum and SkEmptyShader to private

include/core/SkEmptyShader.h

-/*
- * Copyright 2011 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkEmptyShader_DEFINED
-#define SkEmptyShader_DEFINED
-
-#include "SkShader.h"
-
-// TODO: move this to private, as there is a public factory on SkShader
-
-/**
- *  \class SkEmptyShader
- *  A Shader that always draws nothing. Its createContext always returns NULL.
- */
-class SK_API SkEmptyShader : public SkShader {
-public:
-    SkEmptyShader() {}
-
-    virtual size_t contextSize() const SK_OVERRIDE {
-        // Even though createContext returns NULL we have to return a value of at least
-        // sizeof(SkShader::Context) to satisfy SkSmallAllocator.
-        return sizeof(SkShader::Context);
-    }
-
-    SK_TO_STRING_OVERRIDE()
-    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkEmptyShader)
-
-protected:
-    SkEmptyShader(SkReadBuffer& buffer) : INHERITED(buffer) {}
-
-    virtual SkShader::Context* onCreateContext(const ContextRec&, void*) const SK_OVERRIDE {
-        return NULL;
-    }
-
-private:
-    typedef SkShader INHERITED;
-};
-
-#endif